The present invention relates to a structure of an internal combustion engine.
Referring to FIGS. 5 and 6, there is shown a known structure of an internal combustion engine (see JP-U 63-115508 and JP-U 64-6330).
Referring to FIGS. 5 and 6, a chain chamber 65 for receiving a crank chain 64 is defined by a front wall 62 of a cylinder block 61 and a crank chain cover 63 to be attached thereto. The chain chamber 65 serves to return lubricating oil out of two cylinder heads 66 to an oil pan 67, and to lead also blow-by gas within a crank chamber 68 to two head covers 69. A coolant passage 72 is transversely arranged in the chain chamber 65 to fluidly communicate a water pump 70 with a water gallery 71 of the cylinder block 61.
With such known structure of an internal combustion chamber, however, since the coolant passage 72 is transversely arranged in the chain chamber 65, lubricating oil and blow-by gas are refrigerated by coming into direct contact with walls 73 and 74 which define the coolant passage 72, generating water droplets due to condensation of a moisture content contained therein, resulting in production of sludge.
Specifically, when coming into direct contact with the walls 73 and 74 of the coolant passage 72, lubricating oil and blow-by gas are refrigerated to generate water droplets. Nitrogen oxides NO.sub.x in blow-by gas are dissolved in the water droplets, and a following chemical reaction is produced: EQU H.sub.2 O+NO.sub.x =HNO.sub.2, HNO.sub.3
These HNO.sub.2, HNO.sub.3 and unburnt gas HC are reacted in lubricating oil stored in the oil pan 67, generating sludge binder. Carbon, additive, soil and the like mix therewith, finally producing sludge which accumulates in the oil pan 67, causing a deficit in lubricating oil, and a premature deterioration of the engine.